Effects of Changes in Climate and Emissions on Future Particulate Matter Levels and Composition in the United States

The climate chemistry model, CAM-Chem, driven by CCSM3 meteorology, is used to examine the separate and combined effects of changes in climate and emissions on the concentrations and composition of particulate matter(PM) in 2050 over the contiguous United States. The model is first tested in reproducing present-day PM pollution in the United States through comparisons of surface concentrations with U.S. EPA air quality system observations and CASTNET measurements, and composition with IMPROVE measurements. The comparisons show that CAM-Chem model can reproduce the spatial and temporal patterns of PM concentrations and the composition in the United States. The effect of changes in climate during 2000-2050 on particulate matter result in increases in natural emissions including mineral dust and organic aerosols, and increases in the production of PM associated secondary inorganic aerosols. It is projected to increase the levels of particulate matter in 2050 by 0-10 µg/m3 for PM2.5 and 0-14 µg/m3 for PM10 in the eastern and western US, but decrease PM2.5 by 0-6 µg/m3 and 0-10 µg/m3 for PM10 in the central United States. The seasonality of climate change is distinct with stronger effects in summer and weaker in Winter. Simulations based on 2050 climate and emissions show that the changes in anthropogenic emissions decrease PM2.5 by 2-18 µg/m3 and PM10 by 2-22 µg/m3 relative to the climate change alone results. Changes in emissions also affect the PM composition. As a result of changes in anthropogenic emissions, the percentages of inorganic aerosols and elemental carbon decrease in both PM2.5 and PM10 by 2050. Organic aerosols are more affected by climate change than anthropogenic emission change, and the ratio of it in total PM increases following all three IPCC scenarios. Under the IPCC A1FI scenario, the percentages of mineral dust over the eastern and western US increased by 10%-20%. The magnitude of increases in mineral dust decreases under the A1B scenario, and becomes less than 2% under the B1 scenario. The result shows that future change in mineral dust has large uncertainty in affecting U.S. PM level.nd becomes less than 2% under the B1 scenario. The result shows that future change in mineral dust has large uncertainty in affecting U.S. PM level.